Cathode compositions for lithium-ion batteries

ABSTRACT

A cathode composition for a lithium-ion battery having the formula Li[M 1   (1−x) Mn x ]O 2  where 0&lt;x&lt;1 and M 1  represents one or more metal elements, with the proviso that M 1  is a metal element other than chromium. The composition is in the form of a single phase having an O3 crystal structure that does not undergo a phase transformation to a spinel crystal structure when incorporated in a lithium-ion battery and cycled for 100 full charge-discharge cycles at 30° C. and a final capacity of 130 mAh/g using a discharge current of 30 mA/g.

TECHNICAL FIELD

This invention relates to preparing compositions useful as cathodes forlithium-ion batteries.

BACKGROUND

Lithium-ion batteries typically include an anode, an electrolyte, and acathode that contains lithium in the form of a lithium-transition metaloxide. Examples of transition metal oxides that have been used includecobalt dioxide, nickel dioxide, and manganese dioxide. None of thesematerials, however, exhibits an optimal combination of high initialcapacity, high thermal stability, and good capacity retention afterrepeated charge-discharge cycling.

SUMMARY

In general, the invention features a cathode composition for alithium-ion battery having the formula Li[M¹ _((1−x))Mn_(x)]O₂ where0<x<1 and M¹ represents one or more metal elements, with the provisothat M¹ is a metal element other than chromium. The composition is inthe form of a single phase having an O3 crystal structure that does notundergo a phase transformation to a spinel crystal structure whenincorporated in a lithium-ion battery and cycled for 100 fullcharge-discharge cycles at 30° C. and a final capacity of 130 mAh/gusing a discharge current of 30 mA/g. The invention also featureslithium-ion batteries incorporating these cathode compositions incombination with an anode and an electrolyte.

In one embodiment, x=(2−y)/3 and M¹ _((1−x)) has the formulaLi_((1−2y)/3)M² _(y), where 0<y<0.5 (preferably 0.083<y<0.5, and morepreferably 0.167<y<0.5) and M² represents one or more metal elements,with the proviso that M² is a metal element other than chromium. Theresulting cathode composition has the formula Li[Li_((1−2y)/3)M²_(y)Mn_((2−y)/3)]O₂.

In a second embodiment, x=(2−2y)/3 and M¹ _((1−x)) has the formulaLi_((1−y)/3)M³ _(y), where 0<y<0.5 (preferably 0.083<y<0.5, and morepreferably 0.167<y<0.5) and M³ represent one or more metal elements,with the proviso that M³ is a metal element other than chromium. Theresulting cathode composition has the formula Li[Li_((1−y)/3)M³_(y)Mn_((2−2y)/3)]O₂.

In a third embodiment, x=y and M¹ _((1−x)) has the formula M⁴ _(y)M⁵_(1−2y), where 0<y<0.5 (preferably 0.083<y<0.5, and more preferably0.167<y<0.5), M⁴ is a metal element other than chromium, and M⁵ is ametal element other than chromium and different from M⁴. The resultingcathode composition has the formula Li[M⁴ _(y)M⁵ _(1−2y)Mn_(y)]O₂.

The invention provides cathode compositions, and lithium-ion batteriesincorporating these compositions, that exhibit high initial capacitiesand good capacity retention after repeated charge-discharge cycling. Inaddition, the cathode compositions do not evolve substantial amounts ofheat during elevated temperature abuse, thereby improving batterysafety.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view of an electrochemical cell usedto test various electrode compositions.

FIGS. 2(a)-(e) are plots of voltage versus capacity and capacity versuscycle number for the samples described in Examples 1 and 3-6 cycledbetween 4.4 V and 3.0 V.

FIGS. 3(a)-(e) are plots of voltage versus capacity and capacity versuscycle number for the samples described in Examples 1 and 3-6 cycledbetween 4.8 V and 2.0 V.

FIGS. 4(a)-(d) are x-ray diffraction patterns for the samples describedin Examples 3 and 7-9.

FIGS. 5(a)-(d) are x-ray diffraction patterns for the samples describedin Examples 5 and 10-12.

FIGS. 6(a)-(d) are x-ray diffraction patterns for the samples describedin Examples 6 and 16-18.

FIGS. 7(a)-(d) are plots of voltage versus capacity and capacity versuscycle number for the samples described in Examples 6 and 16-18 cycledbetween 4.4 V and 3.0 V.

FIGS. 8(a)-(d) are plots of voltage versus capacity and capacity versuscycle number for the samples described in Examples 6 and 16-18 cycledbetween 4.8 V and 2.0 V.

FIGS. 9(a)-(b) are plots of voltage versus capacity for the samplesdescribed in Examples 19 and 20.

FIG. 10 is a plot of capacity versus cycle number for the sampledescribed in Example 19 cycled between 4.4V and 2.5 V.

FIG. 11 is a plot of capacity versus cycle number for the sampledescribed in Example 20 cycled between 4.4 V and 2.5 V.

FIG. 12 is a plot of capacity versus cycle number for the sampledescribed in Example 1 cycled between 4.4 V and 3.0 V at both 30° C. and55° C.

FIG. 13 is a plot of capacity versus discharge current density for thesample described in Example 1 measured at 30° C. to a 2.5 V cutoff.

DETAILED DESCRIPTION

Cathode compositions have the formulae set forth in the Summary of theInvention, above. The formulae themselves, as well as the choice ofparticular metal elements, and combinations thereof, for M¹-M⁵, reflectcertain criteria that the inventors have discovered are useful formaximizing cathode performance. First, the cathode compositionspreferably adopt an O3 crystal structure featuring layers generallyarranged in the sequence lithium-oxygen-metal-oxygen-lithium. Thiscrystal structure is retained when the cathode composition isincorporated in a lithium-ion battery and cycled for 100 fullcharge-discharge cycles at 30° C. and a final capacity of 130 mAh/gusing a discharge current of 30 mA/g, rather than transforming into aspinel-type crystal structure under these conditions. In addition, tomaximize rapid diffusion in the lithium layers, and thus batteryperformance, it is preferred to minimize the presence of metal elementsin the lithium layers. It is further preferred that at least one of themetal elements be oxidizable within the electrochemical window of theelectrolyte incorporated in the battery.

The cathode compositions may be synthesized by jet milling or bycombining precursors of the metal elements (e.g., hydroxides, nitrates,and the like), followed by heating to generate the cathode composition.Heating is preferably conducted in air at temperatures of at least about600° C., more preferably at least 800° C. In general, highertemperatures are preferred because they lead to materials with increasedcrystallinity. The ability to conduct the heating process in air isdesirable because it obviates the need and associated expense ofmaintaining an inert atmosphere. Accordingly, the particular metalelements are selected such that they exhibit appropriate oxidationstates in air at the desired synthesis temperature. Conversely, thesynthesis temperature may be adjusted so that a particular metal elementexists in a desired oxidation state in air at that temperature.

In general, examples of suitable metal elements for inclusion in thecathode composition include Ni, Co, Fe, Cu, Li, Zn, V, and combinationsthereof. Particularly preferred cathode compositions are those havingthe following formulae:Li[Li_((1−2y)/3)Ni_(y)Mn_((2−y)/3)]O₂;Li[Li_((1−y)/3)Co_(y)Mn_((2−2y)/3)]O₂; andLi[Ni_(y)Co_(1−2y)Mn_(y)]O₂.

The cathode compositions are combined with an anode and an electrolyteto form a lithium-ion battery. Examples of suitable anodes includelithium metal, graphite, and lithium alloy compositions, e.g., of thetype described in Turner, U.S. Pat. No. 6,203,944 entitled “Electrodefor a Lithium Battery” and Turner, WO 00/03444 entitled “ElectrodeMaterial and Compositions.” The electrolyte may be liquid or solid.Examples of solid electrolytes include polymeric electrolytes such aspolyethylene oxide, polytetrafluoroethylene, fluorine-containingcopolymers, and combinations thereof. Examples of liquid electrolytesinclude ethylene carbonate, diethyl carbonate, propylene carbonate, andcombinations thereof. The electrolyte is provided with a lithiumelectrolyte salt. Examples of suitable salts include LiPF₆, LiBF₄, andLiClO₄.

The invention will now be described further by way of the followingexamples.

EXAMPLES

Electrochemical Cell Preparation

Electrodes were prepared as follows. About 21 wt. % active cathodematerial (prepared as described below), 5.3 wt. % Kynar Flex 2801 (avinylidene fluoride-hexafluoropropylene copolymer commercially availablefrom Atochem), 8.4 wt. % dibutyl phthalate, 2.1 wt. % Super S carbonblack (commercially available from MMM Carbon, Belgium), and 63.2 wt. %acetone were mechanically shaken for 1-2 hours in a mixing vial to whicha zirconia bead (8 mm diameter) had been added to form a uniform slurry.The slurry was then spread in a thin layer (about 150 micrometers thick)on a glass plate using a notch-bar spreader. After evaporating theacetone, the resulting film was peeled from the glass and a circularelectrode measuring 1.3 cm in diameter was punched from the film usingan electrode punch, after which the electrode was soaked in diethylether for about 10 minutes to remove dibutyl phthalate and to form poresin the electrode. The ether rinse was repeated two times. The electrodeswere then dried at 90° C. overnight. At the conclusion of the dryingperiod, the circular electrode was weighed and the active mass (thetotal weight of the circular electrode multiplied by the fraction of theelectrode weight made up of the active cathode material) determined.Typically, the electrodes contained 74% by weight active material. Theelectrodes were then taken into an argon-filled glove box where theelectrochemical cell was constructed.

An exploded perspective view of the electrochemical cell 10 is shown inFIG. 1. A stainless steel cap 24 and special oxidation resistant case 26contain the cell and serve as the negative and positive terminalsrespectively. The cathode 12 was the electrode prepared as describedabove. The anode 14 was a lithium foil having a thickness of 125micrometers; the anode also functioned as a reference electrode. Thecell featured 2325 coin-cell hardware, equipped with a spacer plate 18(304 stainless steel) and a disc spring 16 (mild steel). The disc springwas selected so that a pressure of about 15 bar would be applied to eachof the cell electrodes when the cell was crimped closed. The separator20 was a Celgard #2502 microporous polypropylene film(Hoechst-Celanese), which had been wetted with a 1M solution of LiPF₆dissolved in a 30:70 volume mixture of ethylene carbonate and diethylcarbonate (Mitsubishi Chemical). A gasket 27 was used as a seal and toseparate the two terminals.

Elemental Analysis

Approximately 0.02 g of each sample was accurately weighed on amicrobalance (to 1 μg) into a 50 mL glass class A volumetric flask. 2 mLhydrochloric acid and 1 mL nitric acid were then added to form a salt.Once the salt had dissolved, the solution was diluted to 50 mL withdeionized water and the solution shaken to mix. This solution wasdiluted further 10 times. Next, a 5 mL aliquot was removed with a glassclass A volumetric pipet and diluted to 50 mL in a glass class Avolumetric flask with 4% HCl and 2% nitric acid.

The diluted solution were analyzed on a Jarrell-Ash 61E ICP usingstandards of 0, 1, 3, 10, and 20 ppm Co, Ni, Mn, Li, and Na in 4% HCl/2%HNO3. A 5 ppm standard of each element was used to monitor the stabilityof the calibration. All standards were prepared from a certified stocksolution and with class A volumetric glassware. Prior to analysis of theelements, the injector tube of the ICP was cleaned to remove anydeposits. All element calibration curves exhibited r² values in excessof 0.9999.

The analytical results were measured in weight percent. These valueswere then converted to atomic percent and then ultimately to astoichiometry where the oxygen content had been normalized to astoichiometry of 2.

Examples 1-6

Example 1 describes the synthesis of 0.1 mole ofLi[Li_((1−2y)/3)Ni_(y)Mn_((2−y)/3)]O₂ where y=0.416.

12.223 g of Ni(NO₃)₂.6H₂O (Aldrich Chemical Co.) and 13.307 g ofMn(NO₃)₂.4H₂O (Aldrich Chemical Co.) were dissolved in 30 mls ofdistilled water to form a transition metal solution. In a separatebeaker, 9.575 g of LiOH.H₂O (FMC Corp.) was dissolved in 200 mls ofdistilled water. While stirring, the transition metal solution was addeddropwise using a buret to the lithium hydroxide solution over a periodof about 3 hours. This caused the co-precipitation of a Ni—Mn hydroxideand the formation of LiNO₃ (dissolved). The precipitate was recovered byfiltration and washed repeatedly using vacuum filtration. It was thenplaced in a box furnace set to 180° C. to dry, after which it was mixedwith 4.445 g LiOH.H₂O in an autogrinder and pressed into a number ofpellets, each weighing two grams.

The pellets were heated in air at 480° C. for 3 hours, after which theywere quenched to room temperature, combined, and re-ground into powder.New pellets were pressed and heated in air to 900° C. for 3 hours. Atthe conclusion of the heating step, the pellets were quenched to roomtemperature and again ground to powder to yield the cathode material.

Elemental analysis of the cathode material revealed that the compositionhad the following stoichiometry: Li[Li_(0.06)Ni_(0.393)Mn_(0.51)]O₂,which is in close agreement with the target stoichiometry ofLi[Li_(0.06)Ni_(0.42)Mn_(0.53)]O₂.

Examples 2-6 were prepared in analogous fashion except that the relativeamounts of reactants were adjusted to yield samples in which y=0.083(Example 2), 0.166 (Example 3), 0.25 (Example 4), 0.333 (Example 5), and0.5 (Example 6). Elemental analysis of the cathode material from Example5 revealed that the composition had the following stoichiometry:Li[Li_(0.13)Ni_(0.314)Mn_(0.55)]O₂, which is in close agreement with thetarget stoichiometry of Li[Li_(0.11)Ni_(0.33)Mn_(0.56)]O₂.

A powder x-ray diffraction pattern for each sample was collected using aSiemens D5000 diffractometer equipped with a copper target X-ray tubeand a diffracted beam monochromator. Data was collected betweenscattering angles of 10 degrees and 130 degrees.

The crystal structure of each sample was determined based upon the x-raydiffraction data as described in (a) C. J. Howard and R. J. Hill,Australian Atomic Energy Commission Report No. M112 (1986); and (b) D.B. Wiles and R. A. Young, J. Appl. Cryst., 14:149-151 (1981). Latticeparameters were determined using the Rietveld refinement. The latticeparameters for each sample are reported in Table 1. The crystalstructure of each sample could be described well by the O3 crystalstructure type.

Electrochemical cells were constructed according to the above-describedprocedure using the material of Examples 1 and 3-6 as the cathode. Eachcell was charged and discharged between 4.4 V and 3.0 V at 30° C. usingcomputer-controlled discharge stations from Moli Energy Ltd. (MapleRidge, B.C., Canada) and a current of 10 mA/g of active material. FIG. 3is a plot of voltage versus capacity and capacity versus cycle numberfor each cell. Reversible and irreversible capacities were determinedand are reported in Table 1. Each sample showed excellent reversibilityand excellent capacity retention for at least 15 cycles.

A second set of electrochemical cells was constructed using thematerials of Examples 1 and 3-6, and cycled as described above with theexception that the cells were charged and discharged between 4.8 V and2.0 V using a current of 5 mA/g of active material. FIG. 3 is a plot ofvoltage versus capacity and capacity versus cycle number for each cell.Reversible and irreversible capacities were determined and are reportedin Table 1. Each sample performed well. Examples 3 and 4 show largeirreversible capacities, but still give stable reversible capacitiesover 200 mAh/g. Samples 1, 5, and 6 show irreversible capacities lessthan 30 mAh/g and reversible capacities greater than 200 mAh/g. Inparticular, Example 1 shows an irreversible capacity of only about 15mAh/g and a reversible capacity of about 230 mAh/g.

TABLE 1 Rev. Irrev. Rev. Irrev. Capacity Capacity Capacity Capacity HTTa c mAh/g mAh/g mAh/g mAh/g Example y (° C.) (Å) (Å) 3.0-4.4 V 3.0-4.4 V2.0-4.8 V 2.0-4.8 V 1 0.416 900 2.8793 14.2871 160 10 230 15 2 0.083 9002.8499 14.2386 * * * * 3 0.166 900 2.8589 14.2427  82 10 230 120  4 0.25900 2.8673 14.258 117 12 250 50 5 0.333 900 2.8697 14.2654 142 10 240 256 0.5 900 2.8900 14.2971 140 10 200 25 “HTT” refers to the heattreatment temperature. “a” and “c” represent lattice parameters.

Another electrochemical cell was assembled using the material of Example1 and cycled between 3.0 V and 4.4 V using a current of 30 mA/g. Somecycles were collected at 30° C., while other cycles were collected at55° C. The results are reported in FIG. 12. The capacity of the materialwas maintained even at 55° C. after extended cycling, demonstrating thatthe material did not exhibit phase separation after extended cycling.

Another electrochemical cell was assembled using the material of Example1 and used to test the rate capability of the material. Data wascollected at 30° C. up to a 2.0 V cutoff. The results are shown in FIG.13. The results demonstrate that the capacity of the material wasmaintained even up to discharge currents as large as 400 mA/g.

Examples 7-9

Examples 7-9 were prepared following the procedure described forExamples 1-6 where y=0.166 except that the samples were heated at 600°C. (Example 7), 700° C. (Example 8), and 800° C. (Example 9), ratherthan 900° C. X-ray diffraction patterns for each sample were collectedand are shown in FIG. 3, along with an x-ray diffraction pattern forExample 3 prepared at 900° C. The lattice parameters were alsodetermined and are set forth in Table 2, along with the data for Example3. The data demonstrate that as the heating temperature increases, thepeak widths in the diffraction patterns become narrower, indicatingincreased crystallinity. All peaks can be understood based on the O3crystal structure.

TABLE 2 HTT a c Example y (° C.) (Å) (Å) 7 0.166 600 2.8653 14.1739 80.166 700 2.8614 14.2076 9 0.166 800 2.8597 14.2289 3 0.166 900 2.858914.2427 “HTT” refers to the heat treatment temperature. “a” and “c”represent lattice parameters. An asterisk means “not tested”.

Examples 10-12

Examples 10-12 were prepared following the procedure described forExamples 1-6 where y=0.333 except that the samples were heated at 600°C. (Example 10), 700° C. (Example 11), and 800° C. (Example 12), ratherthan 900° C. X-ray diffraction patterns for each sample were collectedand are shown in FIG. 4, along with an x-ray diffraction pattern forExample 5 prepared at 900° C. The lattice parameters were alsodetermined and are set forth in Table 3, along with the data for Example5. The data demonstrate that as the heating temperature increases, thepeak widths in the diffraction patterns become narrower, indicatingincreased crystallinity. All peaks can be understood based on the O3crystal structure.

Electrochemical cells were constructed using material from Examples 10and 12 as the cathode, as cycled as described above. The reversible andirreversible capacities are also reported in Table 3, along with datafor Example 5. All samples performed well.

TABLE 3 Rev. Irrev. Rev. Irrev. Capacity Capacity Capacity Capacity HTTa c mAh/g mAh/g mAh/g mAh/g Example y (° C.) (Å) (Å) 3.0-4.4 V 3.0-4.4 V2.0-4.8 V 2.0-4.8 V 10 0.333 600 2.8800 14.2389 110 50 210 65 11 0.333700 2.8761 14.2569 * * * * 12 0.333 800 2.8714 14.2644 120 20 230 50  50.333 900 2.8697 14.2654 160 10 230 15 “HTT” refers to the heattreatment temperature. “a” and “c” represent lattice parameters. Anasterisk means “not tested”.

Examples 13-15

Examples 13-15 were prepared following the procedure described forExamples 1-6 where y=0.416 except that the samples were heated at 600°C. (Example 13), 700° C. (Example 14), and 800° C. (Example 15), ratherthan 900° C. The lattice parameters were determined for each sample andare set forth in Table 4, along with the data for Example 1 (y=0.416,900° C.). These samples also exhibited the O3 crystal structure.

TABLE 4 HTT a c Example y (° C.) (Å) (Å) 13 0.416 600 2.8829 14.2609 140.416 700 2.8824 14.2720 15 0.416 800 2.8824 14.2808  1 0.416 900 2.879314.2781 “HTT” refers to the heat treatment temperature. “a” and “c”represent lattice parameters.

Examples 16-18

Examples 16-18 were prepared following the procedure described forExamples 1-6 where y=0.5 except that the samples were heated at 600° C.(Example 16), 700° C. (Example 17), and 800° C. (Example 18), ratherthan 900° C. X-ray diffraction patterns for each sample were collectedand are shown in FIG. 6, along with an x-ray diffraction pattern forExample 6 prepared at 900° C. The lattice parameters were alsodetermined and are set forth in Table 5, along with the data for Example6. The data demonstrate that as the heating temperature increases, thepeak widths in the diffraction patterns become narrower, indicatingincreased crystallinity. All peaks can be understood based on the O3crystal structure.

Electrochemical cells were constructed using material from Examples16-18 as the cathode, as cycled as described above. The reversible andirreversible capacities are also reported in Table 5, along with datafor Example 6. In addition, FIG. 7 reports voltage versus capacity andcapacity versus cycle number for each cell, as well as a cellconstructed using Example 6, when cycled between 4.4 V and 3.0 V. FIG. 8reports voltage versus capacity and capacity versus cycle number foreach cell, as well as a cell constructed using Example 6, when cycledbetween 4.8 V and 2.0 V. All samples performed well, with samplesprepared at higher temperatures exhibiting the best capacity retentionand lowest irreversible capacity.

TABLE 5 Rev. Irrev. Rev. Irrev. Capacity Capacity Capacity Capacity HTTa c mAh/g mAh/g mAh/g mAh/g Example y (° C.) (Å) (Å) 3.0-4.4 V 3.0-4.4 V2.0-4.8 V 2.0-4.8 V 16 0.5 600 2.8926 14.298  120 60 200 50 17 0.5 7002.8914 14.2842 140 20 210 25 18 0.5 800 2.8889 14.2812 145 15 210 20  60.5 900 2.8899 14.2964 140 10 200 25 “HTT” refers to the heat treatmenttemperature. “a” and “c” represent lattice parameters.

Examples 19-20

Example 19 describes the preparation of 0.1 mole ofLi[Ni_(y)Co_(1−2y)Mn_(y)]O₂ where y=0.375. The procedure described inExamples 1-6 was followed except that the following reactants were used:10.918 g of Ni(NO₃)₂.6H₂O, 9.420 g of Mn(NO₃)₂.4H₂O, and 7.280 g ofCo(NO₃)₂.6H₂O. In addition, the dried transition metal hydroxide wasmixed with 4.195 g of LiOH.H₂O. The lattice parameters were measured anddetermined to be: a=2.870 Å and c=14.263 Å. Elemental analysis of thematerial revealed that the composition had the following stoichiometry:Li_(1.04)[Ni_(0.368)Co_(0.263)Mn_(0.38)]O₂, which is in close agreementwith the target stoichiometry of Li[Ni₀ ₃₇₅Co_(0.25)Mn₀ ₃₇₅]O₂.

Example 20 was prepared in similar fashion except that the relativeamounts of ingredients were adjusted to yield y=0.25. The latticeparameters were measured and determined to be: a=2.8508 and c=14.206 Å.Elemental analysis of the material revealed that the composition had thefollowing stoichiometry: Li_(1.03)[Ni_(0.243)Co_(0.517)Mn_(0.25)]O₂,which is in close agreement with the target stoichiometry ofLi[Ni_(0.25)Co_(0.05)Mn_(0.25)]O₂

Electrochemical cells were constructed using material from Examples19-20 as the cathode, as cycled as described above. FIG. 9 reportsvoltage versus capacity for each cell when cycled between 2.5 V and 4.8V. Both samples performed well.

A second set of electrochemical cells was constructed using materialfrom Examples 19-20 and cycled as described above between 2.5 V and 4.4V using a current of 40 mA/g. The results are shown in FIGS. 10 and 11.In the case of Example 19 (FIG. 10), data was collected at both 30° C.and 55° C., whereas in the case of Example 20 (FIG. 11) data wascollected at 30° C. only. Both samples performed well.

The cathode material from Example 19 was further analyzed usingdifferential scanning calorimetry (DSC). The sample cell was a 3.14 mmouter diameter, type 304 stainless steel seamless tube having a wallthickness of 0.015 mm that had been cut into an 8.8 mm long piece(MicroGroup, Medway, Mass.). The cell was cleaned, after which one endwas flattened. The flattened end was then welded shut by tungsten inertgas welding using a Miller Maxstar 91 ARC welder equipped with a SnapStart II high frequency ARC starter.

Once the flattened end had been sealed, the tube was loaded in anargon-filled glove box with 2 mg of the cathode material from Example 19taken from a 2325 coin cell that had been charged to 4.2 V using theprocedure described above. The electrolyte was not removed from thecathode sample. After the sample was loaded, the tube was crimped andwelded shut.

The DSC measurements were performed using a TA Instruments DSC 910instrument. The DSC sweep rate was 2° C./minute. Both the onsettemperature and the total heat evolved were recorded. The onsettemperature corresponds to the temperature at which the first majorexothermic peak occurs. The results are shown in Table 6. For the sakeof comparison, data from cathodes prepared using LiNiO₂ and LiCoO₂ isincluded as well. The results demonstrate that cathodes prepared usingthe material from Example 19 exhibited a higher onset temperature andevolved less heat than cathodes prepared using LiNiO₂ and LiCoO₂.

TABLE 6 Material Onset Temperature (° C.) Total Heat (J/g) Example 19290 404 LiNiO₂ 180 1369 LiCoO₂ 185 701

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. A cathode composition for a lithium-ion battery having the formulaLi[M¹ _((1−x))Mn_(x)]O₂ where (a) 0<x<0.5 or (b) 0.5<x<1, and M¹represents one or more metal elements, with the proviso that M¹ is ametal element other than chromium, and when M¹ includes nickel, cobalt,or a combination thereof, all of the nickel has an oxidation state of +2in air, all of the cobalt has an oxidation state of +3 in air, and allof the manganese has an oxidation state of +4 in air, said compositioncharacterized as being in the form of a single phase having an O3crystal structure that does not undergo a phase transformation to aspinel crystal structure when incorporated in a lithium-ion battery andcycled for 100 full charge-discharge cycles at 30° C. and a finalcapacity of 130 mAh/g using a discharge current of 30 mA/g.
 2. A cathodecomposition according to claim 1 wherein M¹ is selected from the groupconsisting of Ni, Co, Fe, Cu, Li, Zn, V, and combinations thereof.
 3. Acathode composition according to claim 1 wherein x=(2−y)/3 and M¹_((1−x)) has the formula Li_((1−2y)/3)M² _(y), where 0<y<0.5 and M²represents one or more metal elements, with the proviso that M² is ametal element other than chromium, and when M² includes nickel, cobalt,or a combination thereof, all of the nickel has an oxidation state of +2in air, all of the cobalt has an oxidation state of +3 in air, and allof the manganese has an oxidation state of +4 in air, said cathodecomposition having the formula Li[Li_((1−2y)/3)M² _(y)Mn_((2−y)/3)]O₂.4. A cathode composition according to claim 3 wherein 0.083<y<0.5.
 5. Acathode composition according to claim 3 wherein 0.167<y<0.5.
 6. Acathode composition according to claim 3 wherein M² is a single metalelement.
 7. A cathode composition according to claim 6 wherein M² is Ni.8. A cathode composition according to claim 1 wherein x=(2−2y)/3 and M¹_((1−x)) has the formula Li_((1−y)/3)M³ _(y), where 0<y<0.5 and M³represents one or more metal elements, with the proviso that M³ is ametal element other than chromium, and when M³ includes nickel, cobalt,or a combination thereof, all of the nickel has an oxidation state of +2in air, all of the cobalt has an oxidation state of +3 in air, and allof the manganese has an oxidation state of +4 in air, said cathodecomposition having the formula Li[Li_((1−y)/3)M³ _(y)Mn_((2−2y)/3)]O₂.9. A cathode composition according to claim 8 wherein 0.083<y<0.5.
 10. Acathode composition according to claim 8 wherein 0.167<y<0.5.
 11. Acathode composition according to claim 8 wherein M³ is a single metalelement.
 12. A cathode composition according to claim 11 wherein M³ isCo.
 13. A cathode composition according to claim 1 wherein x=y and M¹_((1−x)) has the formula M⁴ _(y)M⁵ _(1−2y), where 0<y<0.5, M⁴ is a metalelement other than chromium, and M⁵ is a metal element other thanchromium that is different from M⁴, and when M⁴, M⁵, or both includesnickel, cobalt, or a combination thereof, all of the nickel has anoxidation state of +2 in air, all of the cobalt has an oxidation stateof +3 in air, and all of the manganese has an oxidation state of +4 inair, said cathode composition-having the formula Li[M⁴ _(y)M⁵_(1−2y)Mn_(y)]O₂.
 14. A cathode composition according to claim 13wherein 0.083<y<0.5.
 15. A cathode composition according to claim 13wherein 0.167<y<0.5.
 16. A cathode composition according to claim 13wherein M⁴ is Ni.
 17. A cathode composition according to claim 13wherein M⁵ is Co.
 18. A cathode composition according to claim 13wherein M⁴ is Ni and M⁵ is Co.
 19. A lithium-ion battery comprising: (a)an anode; (b) a cathode according to claim 1, 3, 8, or 13; and (c) anelectrolyte separating said anode and said cathodes.